Income Taxes (Components of deferred tax assets and liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Reserves and allowances	$ 126	$ 87
Debt cancellation and other	11	13
Net operating loss and credit carryforwards	435	192
Total deferred tax assets	572	292
Property and equipment	(1,976)	(1,498)
Intangibles	(237)	(174)
Valuation allowance	(46)	(39)
Total deferred tax liability	(2,259)	(1,711)
Total deferred income tax liability	$ (1,687)	$ (1,419)